This invention relates to a redrawing-ironing apparatus and, more particularly, to an improved redrawing-ironing apparatus in which earing portions can be prevented from being extended too thin into fragments at the end of a redrawing process of a drawn cup.
A drawn-ironed can body which is used extensively of late for carbonated beverage cans, beer cans and the like is usually formed by redrawing and then ironing in two or three steps a drawn cup formed from a metallic blank such as of aluminum alloy sheet or tinplate, on a redrawing-ironing apparatus. The diameter of the cup after redrawing becomes somewhat smaller (the inside diameter being equal to that of the drawn-ironed can body), and its height becomes somewhat larger by redrawing. So as to prevent wrinkles from arising on the bottom during the forming, the cup is redrawn while the inside periphery of its bottom is pushed under fluid pressure between a retainer pad and the surface of a redrawing die.
At the end of the redrawing process, an excessively high pressure is exerted on earing portions of the cup, which are formed usually at 4 to 6 portions circumferentially during the drawing process due to anisotropy of metallic sheets, and, therefore, the earing portion is extended thin and torn off the cup into fragments. Accordingly, the next coming cup is often redrawn with a tool having the fragments sticking thereon, and in such a case, the fragments are embedded in the sidewall portion of the redrawn cup, and the portion of the sidewall portion where the fragments are embedded becomes extremely thin in the process of ironing. Therefore, the sidewall portion tends to develop small holes therein, or completely rupture circumferentially due to tension incidental to the ironing.